Il controllo di qualità nell’impiego della PCR applicata alla determinazione qualitativa dell’HCV-RNA

Detection of hepatitis C virus (HCV) RNA in samples of plasma/serum has become an essential part of the diagnosis and management of HCV-infected patients. Qualitative HCV-RNA tests are used to identify acute HCV infections as well as chronic HCV carriers.In recent years,a variety of commercial and non commercial test systems have been developed for this purpose. Each of these methods is calibrate with proprietary standards and exhibits its own sensitivity (detection limit) and specificity. Obviously, laboratories performing HCV-RNA test should report accurate and reliable results regardless of the type of assay used.Where commercial kit are used for part of or the complete analytical procedure, documented validation points already covered by the kit manufacturer can substitute for the validation by the user.Nevertheless, the performance of the kit with respect to its intended use has to be demonstrated by the user. One of the best ways to assess the performance of individual laboratories for validation of qualitative HCV-RNA test is determine: 1. Specificity. In order to validate the specificity of the analytical procedure, at least 100 HCV-RNA-negative plasma pools should be tested and shown to be non-reactive. 2. Positive cut-off point (detection limit/sensitivity).The positive cut-off point (as defined in the Ph Eur General Method 2. 6. 21) is the minimum number of the target sequences per volume sample which can be detected in 95% of test runs.A dilution series of a working reagent or reference material, which has been calibrated against the WHO HCV International Standard (96/790), should be tested on different days to examine variation between test runs.At least 3 independent dilution series should be tested with a sufficient number of replicates at each dilution to give a total number of 24 test results for each dilution to enable a statistical analysis of the results; 3. Robustness.To demonstrate robustness, at least 20 HCV-RNA negative plasma pools (selected at random) and spiked with HCV-RNA to a final concentration of 3 times the previously determined 95% cut-off value should be tested and found positive; 4. Cross-contamination error.Cross-contamination prevention should be demonstrated by the accurate detection of a panel of at least 20 samples consisting of alternate samples of negative plasma pools and negative plasma pools spiked with high concentrations of HCV (at least 102 x the 95% cut-off value or at least 104 IU/ml).